Intracellular signal transduction is the means by which cells respond to extracellular stimuli. Regardless of the nature of the cell surface receptor (e.g. protein tyrosine kinase or seven-transmembrane G-protein coupled), protein kinases and phosphatases along with phospholipases are the essential machinery by which the signal is further transmitted within the cell [Marshall, J. C. Cell, 80, 179-278 (1995)]. Protein kinases can be categorized into five classes with the two major classes being tyrosine kinases and serine/threonine kinases, depending upon whether the enzyme phosphorylates its substrate(s) on specific tyrosine(s) or serine/threonine(s) residues [Hunter, T., Methods in Enzymology (Protein Kinase Classification) p. 3, Hunter, T.; Sefton, B. M.; eds. vol. 200, Academic Press; San Diego, 1991].
Three major related intracellular pathways, the mitogen-activated kinases, or MAPKs, are now understood to transduce signals from many extracellular stimuli such as environmental stress, infectious agents, cytokines and growth factors. The MAPKs modulate the activity of numerous cell functions such as translocation and activation of transcription factors that control transcription of effector molecules such as cytokines, COX-2, iNOS; the activity of downstream kinases that effect translation of mRNAs; and cell cycle pathways through transcription or modification of enzymes. One of these three major pathways is the p38 MAPK pathway, which refers in most cell types to the isoform p38α which is ubiquitously expressed. The role of p38 in a multitude of functions, particularly related to inflammatory response has been elucidated using selective p38 inhibitors in numerous in vitro and in vivo studies. These functions have been extensively reviewed and a summary can be found in Nature Reviews [Kumar, S. Nature Rev. Drug Discovery, 2:717 (2003)]
Extracellular stimuli such as those described above are generated in a number of chronic diseases which are now understood to have a common underlying pathophysiology termed inflammation. An environmental insult or local cell damage activates cellular response pathways, including but not limited to p38; local cells then generate cytokines and chemokines, in turn recruiting lymphocytes such as neutrophils and other granulocytes. In a secondary response, the consequences include recruitment of additional lymphocytes such as additional phagocytic cells or cytotoxic T cells, and ultimately the adaptive immune response is initiated through activation of T cells. It is not currently fully understood how this acute inflammatory response becomes a chronic response leading to diseases such as rheumatoid arthritis (RA), atherosclerosis, chronic obstructive pulmonary disease (COPD), inflammatory bowel disease (IBD), etc. Nevertheless, the features of inflammation are recognized to contribute to a large number of chronic diseases and pathways such as the p38 pathway are accepted to contribute to the initiation of inflammatory diseases.
For example, atherosclerosis is regarded as a chronic inflammatory disease, which develops in response to injury of the vessel wall and is characterized by the complex development of an occlusive and prothrombotic atheroma. The pathogenesis of this lesion generally involves endothelial dysfunction (reduced bioavailable NO), adhesion molecule expression, adhesion and infiltration of leukocytes, cytokine and growth factor generation, accumulation of foam cells, expansion of extracellular lipid and matrix, activation of matrix metalloproteases (MMPs) and proliferation of vascular smooth muscle cells.
The discovery of p38 (initially termed CSBP, now p38; the isoforms p38α and p38β are the targets of the compounds described) provided a mechanism of action of a class of anti-inflammatory compounds for which SK&F 86002 was the prototypic example. These compounds inhibited IL-1 and TNF synthesis in human monocytes at concentrations in the low uM range [Lee, et al., Int. J. Immunopharmac. 10(7), 835 (1988)] and exhibited activity in animal models which are refractory to cyclooxygenase inhibitors [Lee; et al., Annals N.Y. Acad. Sci., 696, 149 (1993)].
The mechanism by which stress signals (including bacterial and viral infection, pro-inflammatory cytokines, oxidants, UV light and osmotic stress) activate p38 is through activation of kinases upstream from p38 which in turn phosphorylate p38 at threonine 180 and tyrosine 182 resulting in p38 activation. MAPKAP kinase-2 and MAPKAP kinase-3 have been identified as downstream substrates of CSBP/p38 which in turn phosphorylate heat shock protein Hsp27 and other substrates. Additional downstream substrates known to be phosphorylated by p38 include kinases (Mnk1/2, MSK1/2 and PRAK) and transcription factors (CHOP, MEF2, ATF2 and CREB). While many of the signaling pathways required for transduction of stress stimuli remain unknown it appears clear that many of the substrates for p38 listed above are involved. [Cohen, P. Trends Cell Biol., 353-361 (1997) and Lee, J. C. et al, Pharmacol. Ther. vol. 82, nos. 2-3, pp. 389-397, 1999]. There is also emerging evidence that p38 is involved in modulation of the activity of the NF-kB signaling pathway through a role in histone phosphorylation or acetylation, or through reduction of transcription competence of the NF-kB complex [Saccini, S, Nature Immunol., 3: 69-75, (2002); Carter, A B et al J Biol Chem 274: 30858-63 (1999)]. Finally, a role for p38 in generation of response to IFNs through activation by the Type I IFN receptor has been described [Platanias, Pharmacol. Therap. 98:129-142 (2003)]. Activation of p38 is involved in the transcriptional regulation of IFN sensitive genes through modification of specific transcription factors binding to promoter elements in these genes. Direct phosphorylation of STATs by p38 has not been conclusively demonstrated.
In addition to inhibiting IL-1 and TNF upregulation in response to inflammatory stimuli, p38 kinase inhibitors (e.g., SK&F 86002 and SB-203580) are effective in a number of different cell types in decreasing the synthesis of a wide variety of pro-inflammatory proteins including, IL-6, IL-8, GM-CSF, RANTES and COX-2. Inhibitors of p38 kinase have also been shown to suppress the TNF-induced expression of VCAM-1 on endothelial cells, the TNF-induced phosphorylation and activation of cytosolic PLA2 and the IL-1-stimulated synthesis of collagenase and stromelysin. These and additional data demonstrate that p38 is involved not only cytokine synthesis in response to stress, but also in propagating the consequent cytokine signaling [CSBP/P38 kinase reviewed in Cohen, P. Trends Cell Biol., 353-361 (1997)].
Interleukin-1 (IL-1) and Tumor Necrosis Factor (TNF) are important inflammatory cytokines produced by a variety of cells, such as monocytes, macrophages, and smooth muscle cells. IL-1 has been demonstrated to mediate a variety of biological activities thought to be important in immunoregulation and other physiological conditions such as inflammation [See, e.g., Dinarello et al., Rev. Infect. Disease, 6, 51 (1984)]. The myriad of known biological activities of IL-1 include the activation of T helper cells, induction of fever, stimulation of prostaglandin or collagenase production, neutrophil chemotaxis, induction of acute phase proteins and the suppression of plasma iron levels.
There are many disease states in which excessive or unregulated IL-1 production is implicated in exacerbating and/or causing the disease. These include rheumatoid arthritis, osteoarthritis, endotoxemia and/or toxic shock syndrome, other acute or chronic inflammatory disease states such as the inflammatory reaction induced by endotoxin or inflammatory bowel disease; tuberculosis, atherosclerosis, muscle degeneration, cachexia, psoriatic arthritis, Reiter's syndrome, rheumatoid arthritis, gout, traumatic arthritis, rubella arthritis, and acute synovitis. Evidence also links IL-1 activity to diabetes and pancreatic β cells [review of the biological activities which have been attributed to IL-1 Dinarello, J. Clinical Immunology, 5 (5), 287-297 (1985)].
Excessive or unregulated TNF production has been implicated in mediating or exacerbating a number of diseases including rheumatoid arthritis, rheumatoid spondylitis, osteoarthritis, gouty arthritis and other arthritic conditions; sepsis, septic shock, endotoxic shock, gram negative sepsis, toxic shock syndrome, adult respiratory distress syndrome, cerebral malaria, chronic obstructive pulmonary disease, silicosis, pulmonary sarcoisosis, bone resorption diseases, reperfusion injury, graft vs. host reaction, allograft rejections, fever and myalgias due to infection, such as influenza, cachexia secondary to infection or malignancy, cachexia, secondary to acquired immune deficiency syndrome (AIDS), AIDS, ARC (AIDS related complex), keloid formation, scar tissue formation, Crohn's disease, ulcerative colitis, or pyresis.
Inflammatory diseases are also marked by increases in IL-6 and C-reactive protein (CRP), both of which are sensitive to inhibition by p38 inhibitors. IL-6 stimulation of CRP production is directly inhibited by p38 inhibitors in human vascular endothelial cells, and CRP is produced by hepatocytes in response to IL-6. CRP is considered a major risk factor for cardiovascular disease [Circulation 2003. 107: 363-369] and may be a significant independent risk factor for chronic obstructive pulmonary disease [Circulation 2003. 107:1514-1519]. IL-6 is also upregulated in endometriosis [Bedaiwy et al., 2002, Human Reproduction 17:426-431; Witz, 2000, Fertility and Sterility 73: 212-214].
Interleukin-8 (IL-8) and RANTES are chemotactic factors produced by several cell types including mononuclear cells, fibroblasts, endothelial cells, epithelial cells, neutrophils and T cells. Chemokine production is induced by pro-inflammatory stimuli such as IL-1, TNF, or lipopolysaccharide (LPS), or viral infection. IL-8 stimulates a number of functions in vitro. It has been shown to have chemoattractant properties for neutrophils, T-lymphocytes, and basophils. In addition it induces histamine release from basophils from both normal and atopic individuals as well as lysozomal enzyme release and respiratory burst from neutrophils. IL-8 has also been shown to increase the surface expression of Mac-1 (CD 11b/CD 18) on neutrophils without de novo protein synthesis, which may contribute to increased adhesion of the neutrophils to vascular endothelial cells. Many diseases are characterized by massive neutrophil infiltration. Conditions such as chronic obstructive pulmonary disease associated with an increase in IL-8 production would benefit by compounds which are suppressive of IL-8 production. RANTES is produced by cells such as epithelial cells and airway smooth muscle in response to infection or cytokine stimulation. Its main chemoattraction is for T cell subtypes and blood-borne monocytes.
IL-1, TNF and other cytokines affect a wide variety of cells and tissues and these cytokines as well as other leukocyte derived cytokines are important as critical inflammatory mediators of a wide variety of disease states and conditions. The inhibition of these cytokines is of benefit in controlling, reducing and alleviating many of these disease states.
In addition to the involvement of p38 signaling in the production of IL-1, TNF, IL-8, IL-6, GM-CSF, COX-2, collagenase and stromelysin, signal transduction via CSBP/p38 is required for the effector functions of several of these same pro-inflammatory proteins plus many others. For example, growth factors such as VEGF, PDGF, NGF signal through surface receptors which in turn activate cellular signaling pathways including p38 MAPK [Ono, K. and Han, J., Cellular Signalling, 12 1-13 (2000); Kyriakis, J M and Avruch, J. Physiol Rev 81: 807-869 (2001)]. TGFχ, a key molecule in the control of inflammatory response, also activates p38 as a consequence of engagement of the TGFβ receptor. The involvement of CSBP/p38 in multiple stress-induced signal transduction pathways provides additional rationale for the potential utility of CSBP/p38 in the treatment of diseases resulting from the excessive and destructive activation of the immune system, or chronic inflammation. This expectation is supported by the potent and diverse activities described for CSBP/p38 kinase inhibitors [Badger, et al., J. Pharm. Exp. Thera. 279 (3): 1453-1461, (1996); Griswold, et all Pharmacol. Comm. 7, 323-229 (1996); Jackson, et al., J. Pharmacol. Exp. Ther. 284, 687-692 (1998); Underwood, et al., J. Pharmacol. Exp. Ther. 293, 281-288 (2000); Badger, et al., Arthritis Rheum. 43, 175-183 (2000)].
Chronic inflammation is also characterized by ongoing remodeling and repair of affected tissue, leading in some cases to excess fibrotic tissue. A role for p38 MAPK in fibrosis is supported by findings that this enzyme mediates signaling of transforming growth factor beta (TGF-β) on markers and proteins of fibrosis. For example, it has been shown that TGF-β increases the kinase activity of p38 MAPK through the TGF-β activated kinase TAK-1 (Hanafusa et al., 1999, J. Biol. Chem. 274:27161-27167). Furthermore, the p38 inhibitor SB-242235 inhibited the TGF-β-induced increases in fibronectin and thrombospondin (Laping et al., 2002, Molec. Pharmacol. 62:58-64). These results show that p38 MAPK is a key signaling intermediate for the effect of the pro-fibrotic cytokine TGF-β on components of the extracellular matrix and markers of fibrosis.
P38 also plays a role in directing survival and apoptosis of cells in response to various stimuli. Both survival and apoptosis can be p38 regulated depending on the stimulus and the cell type [Morin and Huot, Cancer Research. 64:1893-1898 (2004)]. For example, TGF-beta can stimulate apoptosis in murine hepatocytes through activation of gadd45b, a protein involved in cell-cycle control, in a p38 mediated process [Yoo et al, J. Biol. Chem. 278:43001-43007, (2003)]. In a different response pathway, UV-stress can activate p38 and trigger apoptosis of a damaged cell. P38 has also been shown to promote survival of lymphocytes in response to stress, including neutrophils and CD8+ T cells.
There remains a need for treatment, in this field, for compounds which are cytokine suppressive anti-inflammatory drugs, i.e. compounds which are capable of inhibiting the CSBP/p38/RK kinase. The present invention is directed to such novel compounds which are inhibitors of p38 kinase.